This is from the Alexa Pro service -- the one you pay for.
The cart is for the subject sample tubes' Global Ranks -- which are relative to one another in their methodology.
There is no traffic volume computation given you would have to extrapolate that from some known reference points and there is no guarantee of that being objective or subjective anyway.
According to this graph of the past 6 months rankings notwithstanding tubecup.com there are no real changes evidenced by traffic ranking changes.
You can try quantcast estimates of traffic volume but they are off in real terms but they serve for a comparison only.
Tubecup has a questionable variance in traffic volume between the two sources.
Conclusion: Contradictory statistics with no reliable trending.